What methods can I use to determine the in-place strength of concrete for formwork removal?
A. ACI 318-051 and ACI 301-052 require field-cured cylinder tests to determine if the concrete has reached the strength specified by the engineer for removal of formwork or shoring. The documents, however, also allow the use of alternative methods when approved by the building official. These alternative methods are given in the commentary to Section 6.2 of ACI 318-05 and Section 2.3.4.2 of ACI 301-05 and include tests of cast-in-place cylinders, penetration resistance tests, pullout tests, and the maturity method. Measurements from the alternative methods, except cast-in-place cylinders, must be correlated to compressive strength data using project materials. If the method, testing equipment, project materials, or mixture proportions change during the project, a new correlation that may take several days or weeks must be conducted. Methods to correlate the data, implement the in-place testing program, and interpret and report the results for each of the alternative methods are discuss
